The present invention relates to a cylinder head gasket formed of one metal plate and provided with a partial resin coating around a hole to be sealed.
A cylinder head gasket for sealing between a cylinder head and a cylinder block generally includes holes for cylinder bores, oil holes, water holes, and bolt holes. Also, in order to seal combustion gases generated in the combustion chambers, oil circulating through an oil gallery and water in a water jacket, the gasket includes sealing means, such as beads and seal rings, for providing adequate sealing pressures for the respective holes to be sealed.
Especially, since high temperature and high pressure combustion gases are generated in the holes for the cylinder bores when the engine is operated, sealing around the holes for the cylinder bores is especially important. Therefore, a metal plate superior in mechanical strength and durability is used, and for example, a plurality of metal plates is laminated, and beads are arranged around the holes for the cylinder bores to provide high sealing pressures by the beads.
Also, in order to protect creep relaxation of the beads and increase the surface pressures around the holes for the cylinder bores, various methods are taken. For example, a second metal plate with a stopper bead inside or outside the bead is arranged, a stopper as a metal shim is disposed, or a plate having a half bead or full bead is combined.
On the other hand, recently, a head gasket is required to manufacture at a low cost. If the gasket is formed of a plurality of metal plates, it can not respond to a cost reducing demand. Thus, it has been considered to use a gasket formed of one metal plate.
However, in the head gasket formed of one metal plate, a plurality of sealing means can not be combined, as used in the gasket formed of a plurality of metal plates, and sealing means is limited. Therefore, in the head gasket requiring high sealing ability and durability, it is difficult to provide secure sealing.
For this purpose, it is considered to install a reinforcing shim made of metal, provide a grommet or increase the thickness by thermal spraying around a hole for the cylinder bore. If these processings are made, the manufacturing steps and raw materials are increased to increase the cost. Thus, these processings are required to be deleted.
On the other hand, the engine has been made light, so that the cylinder head and the cylinder block are formed of relatively soft aluminum alloy. Therefore, in case a cylinder head gasket is disposed between the cylinder head and the cylinder block, and is tightened strongly to keep the sealing ability, when the engine vibrates and a thermal expansion is applied, the cylinder block and cylinder head may be damaged by the gasket. The combustion gas may leak through the damaged portion.
In case the contact of the bead of the gasket with the engine parts, such as cylinder head, is a direct metal contact, a small space or gap is formed by the projections and dents due to a tool mark on the surface of the engine parts, vibration of the engine or thermal changes of the gasket and the engine parts. Combustion gas with high temperature and pressure may leak through the small space or gap.
If the combustion gas with high temperature and pressure leaks, the combustion gas is likely to enter into the oil hole and water hole through the space between the head gasket and the engine part. When the combustion gas enters the oil hole and water hole to cause air inclusion, it causes a trouble in circulation of oil and water, leading to a serious engine trouble. It is, therefore, important to prevent the leakage of the combustion gas.
The present invention has been made to obviate these problems, and an object of the invention is to provide a cylinder head gasket formed of one metal plate, which can provide a sufficient sealing ability.
Another object of the invention is to provide a cylinder head gasket as stated above, wherein the gasket does not hurt the cylinder head and the cylinder block.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A cylinder head gasket for an internal combustion engine of the invention is formed of one metal plate having a base portion extending substantially throughout an entire area to be sealed, a hole formed in the base portion corresponding to a hole of the engine, and a bead surrounding the hole. A resin coating is deposited on at least a part of the bead of the metal plate on a projection side and/or a recess side. The resin coating may be applied to cover the entire bead on at least one of the projection side and the recess side of the bead.
The resin coating may have, according to the object of regulating the surface pressure, an equal thickness or unequal thickness. In case of the unequal thickness, the resin coating may have one layer with different thicknesses, or have a plurality of layers so that the thickness is changed by the number of the layers.
In the cylinder head gasket, the resin coating is formed to at least cover a part of the bead to have a function of reinforcing the bead. In addition, since the resin coating which is softer than a metal shim and harder than a rubber coating exhibits the sealing ability, the sealing ability of the gasket with respect to a cylinder head and a cylinder block is improved. Since the resin coating operates as an absorbing material, the damage and creep relaxation of the bead are protected, and the durability of the gasket is improved.
In case the resin coating is applied to both ends of the bead while covering the bead, since the step portions of the resin coating at both ends thereof form second and third seal lines, the sealing ability for the combustion gas is further improved.
Incidentally, it is difficult to fix a metal shim to cover a main bead with a projection, and a thermal sprayed shim is not good for accurate processing and is expensive. Even if the thermal sprayed shim is formed accurately, since metal is harder than the resin, it can not provide good sealing ability. Also, the shim can not operate as an absorbing material.
Also, in case a material, such as gum layer softer than the resin is used, the material may flow or break in use by pressure. Therefore, it can not provide the sealing function nor absorbing ability like the resin. Also, since a soft material can not provide a step because of its softness, the second and third sealing lines can not be formed inside and outside the bead.
In the above gasket, the resin coating has the hardness of F to 6H in pencil hardness. If the resin coating is softer than F in pencil hardness, the resin coating may flow or break by the pressure applied thereto. If the resin layer is harder than 6H in pencil hardness, the sealing and absorbing abilities become bad. Therefore, the resin coating is preferably formed to have the hardness of F to 6H in pencil hardness.
In the gasket of the invention, the resin coating is formed of epoxy resin, phenol resin, phenoxy resin, fluoroplastics and polyamideimido, or combination thereof. Although the resin coating may be formed of various resins, it is preferable to use epoxy resin, phenol resin, phenoxy resin, fluoroplastics, polyamideimido, or combination thereof in view of the hardness and easy application. Especially, the phenoxy resin has heat resistance over 200xc2x0 C., and in view of working ability and physical characteristics in coating, it is most preferable to use the phenoxy resin.
In the invention, the resin coating is applied by screen printing. Although the resin coating may be applied freely in various shapes by spraying using a mask, the resin coating can be easily formed even in a complicated shape if the screen printing is used. Further, by multiple printings, the resin coating can be formed easily with different thicknesses. Thus, it is possible to easily form the resin coating with adequate thickness according to the position thereof. Also, it is possible to form the resin coating with various shapes and thicknesses, and to have a multiple structure with different materials by the multiple printings.
The gasket may have additional gum coatings on the metal plate with the resin coating to improve affinity with the cylinder head and the cylinder block.